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Eukaryotic Cell, June 2004, p. 685-694, Vol. 3, No. 3
1535-9778/04/$08.00+0 DOI: 10.1128/EC.3.3.685-694.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Paul R. Lindstrom,
Alison E. Meyer,1,
and Kathleen M. Karrer*
Department of Biological Sciences, Marquette University, Milwaukee, Wisconsin 53201
Received 3 November 2003/ Accepted 22 March 2004
Three insertion elements were previously found in a family of germ line-limited mobile elements, the Tlr elements, in the ciliate Tetrahymena. Each of the insertions contains an open reading frame (ORF). Sequence analysis of the deduced proteins encoded by the elements suggests that they are homing endonucleases. The genes are designated TIE1-1, TIE2-1, and TIE3-1 for Tetrahymena insertion-homing endonuclease. The endonuclease motif occupies the amino terminal half of each TIE protein. The C-terminal regions of the proteins are similar to the APETELA2 DNA binding domain of plant transcription factors. The TIE1 and TIE3 elements belong to families of repeated sequences in the germ line micronuclear genome. Comparison of the genes and the deduced proteins they encode suggests that there are at least two distinct families of homing endonuclease genes, each of which appears to be preferentially associated with a specific region of the Tlr elements. The TIE1 and TIE3 elements and their cognates undergo programmed elimination from the developing somatic macronucleus of Tetrahymena. The possible role of homing endonuclease-like genes in the DNA breakage step in developmentally programmed DNA elimination in Tetrahymena is discussed.
Present address: Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, TN 38105.
Present address: 3028A S. 47th St., Milwaukee, WI 53219.
Present address: Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53705-1544.
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